In　order　to　enhance　the　security　of　vehicular　ad　hoc　networks　(VANETs).　By　dividing　the　roadside　units　(RSUs)　into　application-RSUs　(AP-RSUs)　and　authentication-RSUs　(AU-RSUs)　in　application　layer,　we　give　a　new　security　scheme　for　VANETs.　This　functional　division　of　RSUs　makes　VANETs　more　logically　clear.　AU-RSUs　record　vehicles＇　real　identities　and　assign　temporary　certificates　to　them.　The　temporary　certificates　can　help　vehicles　hide　their　real　identities.　Hence,　the　scheme　not　only　can　guarantee　the　vehicle　anonymity,　but　also　can　realize　the　vehicle　traceability.